1. Field of the Invention
The present invention relates to a device for detecting an angular displacement relative to absolute space by utilizing inertial force and, more specifically, to an angular displacement detecting device suitable for use in, for example, detecting an image shake which may occur during photography using a camera.
2. Description of the Related Art
A conventional angular displacement detecting device of this type is basically constructed as described below in detail, as disclosed in U.S. Pat. application Ser. No. 355,330, filed on May 23, 1989, and Japanese Laid-open Patent Application Nos. Hei 2.82165 and Hei 2-102414. The construction will be explained with reference to FIGS. 37 to 39.
As shown in these figures, the conventional angular displacement detecting device comprises a base 401 to which individual parts for constituting the device are secured in position, and a tubular casing 402 serving as a sealed liquid container having a chamber in which a floating body 403 and a liquid 404 are sealed. The tubular casing 402 has a groove 402a which is formed in its inner wall so as to securely engage with a floating-body support 414 having a U-like cross section as shown in detail in FIG. 39. The floating body 403 has magnetic characteristics, and is supported for rotation about an axis 403a by the floating-body support 414. Mirrors 409 are respectively secured to one pair of opposed side faces of the central block of the floating body 403, and each of the mirrors 409 is covered by a mask 410 having a slit 410a. Arms 403b extend from the other pair of opposed side faces of the central block, respectively. The floating body 403 is constructed so as to maintain the balance of rotation about the axis 403a and the balance of buoyancy in the liquid 404. In addition, the floating body 403 has magnetic characteristics.
The liquid 404 which is sealed in the tubular casing 402 is a transparent liquid. A light emitting element (iRED) 405, which is adapted to emit light by energization, is secured to the base 401 via a light-emitting-element carrier 407. A light receiving element (PSD) 406 utilizes a photoelectric conversion device whose output varies with the position where light is received, and is fixed to the base 401 via a light-receiving-element carrier 408. The light emitting element 405 and the light receiving element 406 constitute optical angular displacement detecting means of the type which transmits light by means of either of the mirrors 409 secured to the opposed side faces of the central block of the floating body 403. A light guide portion 407a is formed on the light-emitting-element carrier 407 for guiding light emitted from the light emitting element 405, and a mask 410' is secured to the distal end of the light guide portion 407a. The mask 410' has a slit 410a' identical to the slit 410a of the mask 410. Since the light transmission is effected through the tubular casing 402, the whole of the tubular casing 402 or the part of the same upon which light falls is formed of a transparent material.
A pair of yokes 419 and 420 is disposed in such a manner as to produce a magnetic field action for holding the floating body 403 having the magnetic characteristics in a fixed position, i.e., in a position where the floating body 403 takes the shown attitude. Ends 419a and 420a of the respective yokes 419 and 420 are opposed to and spaced apart from each other along the diameter of the tubular casing 402 as shown in FIG. 37. A yoke 421 is interposed between the other end portions of the yokes 419 and 420, and a solenoid coil 422 is fitted onto the yoke 421. The above-described arrangement allows a magnetic circuit to be formed by the yokes 419, 420 and 421 and the floating body 403, and a magnetic force is imparted to the floating body 403 by the magnetic force produced by the solenoid coil 422.
The above-described rotatable supporting of the floating body 403 is accomplished in the following manner. As shown in FIG. 38 in cross-sectional form, a rotary shaft 411 extends through the central block of the floating body 403 in the vertical direction, and a pivot 412 having an outwardly pointed end is press-fitted into each of the top and bottom ends of the rotary shaft 411. Pivot bearings 413 are respectively secured to the upper and lower arms of the U-like shape of the above-described floating body support 414 in such a manner that they are opposed to each other in the inward direction. The floating body 403 is supported by the engagement between the pointed ends of the pivots 412 and the corresponding pivot bearings 413.
A lid 415 is bonded to the tubular casing 402 in a sealed manner by a known art utilizing a silicone adhesive or the like. A packing rubber 416 is sandwiched between a pressure disk 417 and the lid 415, and is fixed by screws or the like.
In the above-described arrangement, the floating body 403 is constructed so that the balance of rotation about the axis 403a and the balance of buoyancy in the liquid 404 can be maintained as described previously in order to prevent an angular moment from occurring by the influence of gravitation whatever attitude the floating body 403 may take, and to prevent substantial loads from acting on the pivots or the pivot bearings.
According to the above-described arrangement, even if the tubular casing 402 rotates about the rotational axis 403a, an inner portion of the liquid 404 does not move owing to inertia and, therefore, the floating body 403 which is in a floating state does not rotate. As a consequence, the tubular casing 402 and the floating body 403 rotate about the rotational axis 403a with respect to each other. This is the principle of the device for detecting a relative angular displacement, and the relative angular displacement can be detected by the optical detecting means utilizing the light emitting element 405 and the light receiving element 406.
In practice, a flow is produced in the inner portion of the liquid 404 by the influence of the wall surface of the tubular casing 402, and the flow applies a viscosity force to the floating body 403. The influence of the flow, however, can be minimized by appropriately selecting factors such as the distance between the wall surface and the floating body 403 and the viscosity of the liquid 404.
In the device having the above-described arrangement, detection of an angular displacement is performed in the following manner.
Light emitted from the light emitting element 405 passes through the light guide 407a and illuminates the floating body 403, and light reflected by an illuminated one of the mirrors 409 reaches the light receiving element 406. As described above, the mask 410, is secured to the distal end of the light guide 407a, while the mask 410 is secured to each of the mirrors 409 of the floating body 403. Accordingly, the light is approximately collimated by the slit 410a of the mask 410 during light transmission, whereby a sharply focused image (slit image) is formed on the light receiving element 406.
The tubular casing 402, the light emitting element 405 and the light receiving element 406 integrally move since all of them are secured to the base 401. If a relative angular displacement occurs between the tubular casing 402 and the floating body 403, the slit image on the light receiving element 406 will move by an amount corresponding to the relative angular displacement. Accordingly, the light receiving element 406, which utilizes a photoelectric conversion device whose output varies with the position where light is received, produces an output substantially proportional to the positional displacement of the slit image. It is, therefore, possible to detect the angular displacement of the tubular casing 402 by utilizing such an output as information.
In the case of the angular displacement detecting device having the above-described arrangement, since no external force is applied to the floating body 403, the attitude of the floating body 403 cannot be restricted. As a result, it might be considered impossible to ensure that the slit image is positioned within the measurement range of the light receiving element 406. However, if, for example, the above-described solenoid coil 422 is used to exert a weak magnetic field action on the floating body 403, the magnetic field action can be made to act as a spring force which produces a force locating the floating body 403 at the steady position shown in FIG. 37.
The spring force exerted on the floating body 403 by the magnetic field action is theoretically a force which maintains the floating body 403 in a fixed attitude with respect to the tubular casing 402, i.e., a force which acts to move the floating body 403 integrally with the tubular casing 402. If such spring force is excessively strong, the tubular casing 402 and the floating body 403 will move integrally, thus resulting in the problem that a relative angular displacement required for a desired angular displacement is not produced. However, if the magnetic field action is made sufficiently small with respect to the inertia of the liquid 404, it is possible to realize an arrangement capable of responding to an angular displacement of relatively low frequency as well.
In the above-described arrangement, the floating body 403 is subject to a force acting to move it in the direction in which the magnetic resistance of the magnetic field produced by the coil 422 is reduced. In other words, the floating body 403 tends to move so as to reduce such magnetic resistance in a closed magnetic path formed among the floating body 403, the yoke 419, the yoke 421, the yoke 420 and the floating body 403. More specifically, when the end 419a of the yoke 419, the longitudinal axis of the floating body 403 and the end 420a of the yoke 420 are aligned as shown in FIG. 37, the magnetic resistance reaches its minimum. Accordingly, if a displacement occurs in this state, a force acts to return the floating body 403 to its original position.
Although several modifications are proposed in the above noted patent applications, each is basically identical to the above-described arrangement in that a magnetic force acts as a spring force in the fixed direction determined by the arrangement of yokes which form part of a closed magnetic path.
The liquid 404 sealed in the tubular casing 402 is required to have light transmission properties, low viscosity and high specific gravity. The light transmission properties are indispensable for realizing position detection utilizing light emitting and receiving elements. The viscosity of the liquid 404 tends to cooperate with the wall surface of the tubular casing 402 to integrally move the tubular casing 402 and the floating body 403, resulting in accuracy deterioration. However, if the viscosity of the liquid 404 is small, the resultant force will be small and accuracy will be improved. Further, if the viscosity is small, the gap between the wall surface of the tubular casing 402 and the floating body 403 can be made small, whereby the arrangement can be made compact. The above explanation also applies to the high specific gravity. Since the detecting device utilizes inertia, it is a matter of course that as the inertia increases, the accuracy improves. The high specific gravity also contributes toward realizing a compact arrangement.
As is apparent from the foregoing, limitations imposed on the liquid 404 are strict and the performance and size of the device are greatly influenced by the liquid 404. One example of liquids having relatively good characteristics within such limitations is a fluorine-contained inactive liquid having a specific gravity of approximately 1.8. If the floating body 403 is formed of a material corresponding to this specific gravity, for example, PBT (polybutylene terephthalate) which is a plastics material containing iron powder, the content of iron power is approximately 30 percent by weight and approximately 7 percent by volume. Accordingly, since the floating body 403 only contains approximately 7 percent of iron powder, its magnetic permeability is extremely low. In other words, the magnetic resistance of the closed magnetic path formed among the floating body 403, the yoke 419, the yoke 421, the yoke 420 and the floating body 403 is extremely high, and the force exerted on the floating body 403 by the magnetic field produced by the solenoid coil 422 is extremely weak. The result is a low-efficiency electromagnetic conversion which may lead to high power consumption.